The present invention relates to a system, method and apparatus for ablating tissue under temperature control of each electrode to control lesion dimensions, and in particular for ablating myocardial tissue to treat Ventricular Tachycardia (VT) or atrial fibrillation/flutter (AF).
Ventricular tachycardia is a disease of the heart which causes the heart chambers to beat excessively fast and usually degenerates to ventricular fibrillation where the heart chambers do not effectively pump blood through the body""s system and hence leads to death. Ventricular tachycardia is the most common cause of cardiac arrest and sudden death. Typical features of patients with VT are (1) a history of myocardial infarction (heart attack), (2) significant left ventricular dysfunction (the main chamber effecting the pumping action), and (3) left ventricular aneurysm (dilation, thinning and stretching of the chamber). Detailed mapping studies of the electrical propagation within the myocardium during VT have shown that a re entrant pathway within and around the scarring (caused by infarction) is responsible for the arrhythmia, These studies have shown that the critical area of myocardium necessary to support reentry appears to be less than 2 to 4 cm2.
Atrial fribillation (AF) and atrial flutter are diseases of the heart which can cause the heart to beat excessively fast and frequently in an erratic manner. This usually results in distress for patients. This may also be associated with clot formation in the atria, which may become dislodged and cause strokes. AF is usually due to abnormal electrical activation of the atria. Preliminary investigations have shown that linear lesions in the atria using radiofrequency ablation can cure these arrhythmias.
A number of conventional techniques using radio frequency (RF) energy have been used to treat VT or AF. Endocardial radio frequency catheter ablation has been used in the treatment of hemodynamically stable monomorphic ventricular tachycardia secondary to coronary artery disease. The resulting lesions caused in RF ablation using catheters however have been insufficient in volume to destroy the area of tissue causing the arrhythmia.
Radiofrequency catheter ablation on has been used for treatment of AF but has been limited by the number of separate ablationis required and the time required to perform the procedure.
In accordance with one conventional technique, RF energy is delivered from an RF source, incorporating phase shift networks to enable potential differences and hence current flow between multiple, separate electrode structures Also, multiple RF power sources have been used connected to such electrodes. The independent phases of the power source lead to multiple current paths.
However, this conventional system lacks adequate temperature cntrol because the multiphase RF ablation cannot function satisfactorily unless certain restrictions on the dimensions of the electrode are adhered to. The ablation temperature can only be maintained at an optimum predetermined level of approximately 80xc2x0 C. This is a significant shortfall of the technique.
The present invention is directed to improving the efficacy of producing radio frequency lesions using multiple temperature controlled delivery by splitting high frequency current from a single generator into a number of electrodes simultaneously. Further, the system accurately measures the temperatures of these electrodes which are then used as the feedback in the system, allowing appropriate control strategies to be performed to regulate the current to each electrode.
In accordance with a first aspect of the invention, a system for ablating tissue comprises:
a device for generating RF energy;
a probe device comprising N separate electrodes, each having a corresponding device for sensing the temperature of the electrode;
a splitter device for splitting the RF energy coupled to the generating device and the probe device, the splitter device having N separate channels each being coupled to a corresponding one of the N electrodes and temperature sensing device; and
a device for controlling the splitter device, whereby the ablation of tissue at each electrode is independently controlled using closed loop feedback of the temperature of the electrode by independently regulating the amount of the RF energy delivered to each electrode.
Preferably, the system comprises a plurality of the probe devices and the splitter devices, and the controlling device separately controls each of the probe devices and the corresponding splitter device.
Preferably, the probe device has an elongated needle-like structure with one end adapted to puncture tissue and having sufficient rigidity to puncture the tissue, or a catheter which can be advanced into the heart. Each of the electrodes may consist of a circular metal surface separated one from another by insulation.
Preferably, the RF energy has a single phase.
Preferably, the system further comprises a device for independently and continuously adjusting the RF energy delivered to each electrode in response to a control signal from the controlling device dependent on the temperature of the electrode.
Preferably, the controlling device is programmable.
Optionally, the probe device is a catheter probe device.
Preferably, each of the temperature sensing devices is a thermocouple. Preferably, the splitter device comprises one or more devices for independently interrupting current from the RF energy generating device to a respective electrode.
In accordance with a second aspect of the invention, a medical apparatus for treatment by radiofrequency ablation of tissue comprises:
an RF energy generator;
one or more probes each comprising a pIurality of separate electrodes and corresponding temperature sensors for sensing the termperature of the electrodes, each temperature sensor connected to a respective one of the plurality of electrodes;
a splitter for splitting the RF energy provided by the RF energy generator, the splitter having a plurality of separate channels, wherein each of the electrodes is coupled to a respective one of the plurality of channels; and
a programmable controller coupled to the RF splitter for independently controlling the ablation of tissue at each electrode using closed loop feedback of the temperature of the electrode, whereby the amount of the RF energy delivered to each electrode is independently regulated by the programmable controller.
In accordance with a third aspect of the invention, a radio frequency energy splitter for use with one or more probes in a system for RF ablation of tissue is provided. Each probe comprises a plurality of separate electrodes and corresponding temperature sensors for sensing the temperature of the electrode. The splitter comprises:
an input device for receiving RF energy from an RF energy generator;
a plurality of channel modules for separately delivering RP energy from the input device to a respective electrode of the plurality of electrodes of the one or more probes, each channel module comprising:
a device for variably adjusting an amount of the RF energy delivered to the respective electrode in response to a control signal, the variable adjusting device being coupled between the input device and the respective electrode;
a device for interrupting the RF energy delivered to the respective electrode;
an output device coupled to the respective temperature sensor for providing a temperature signal;
a device for determining if the temperature at the respective electrode exceeds a predetermined threshold and actuating the interrupting device if the threshold is exceeded, whereby the RF energy is interrupted from delivery to the respective electrode;
wherein each channel module is capable of receiving the respective control signal from and providing the respective temperature signal to a programmable controller so that the amount of the RF energy delivered to each electrode can be independently regulated using closed loop feedback of the temperature of each electrode.
Preferably, the variable adjusting device or circuit comprises a bridge rectifier including a fast-switching variable resistance for controlling operation of the bridge rectifier in response to the control signal.
Preferably, the RF energy interrupting device comprises a circuit for interrupting a current through the RF energy interrupting device and a circuit for limiting the current.
Preferably, the determining device compares the temperature signal with the predetermined threshold.
In accordance with a fourth aspect of the invention, a method for ablating tissue comprises the steps of:
generating RF energy;
providing a probe device comprising N separate electrodes, each having a corresponding temperature sensing device;
measuring the temperature of each electrode using the temperature sensing device of the electrode;
splitting the RF energy to the probe device into N separate channels each being coupled to a corresponding one of the N electrodes and temperature sensing device; and
controlling the splitting of the RF energy to the probe device, whereby the ablation of tissue at each electrode is independently controlled using closed loop feedback of the measured temperature of the electrode by independently regulating the amount of the RF energy delivered to each electrode.
Preferably, the method comprises the step of separately controlling the splitting of the RF energy to a plurality of the probe device.
Preferably, the probe device has, an elongated needle-like structure with one end adapted to puncture tissue and having sufficient rigidity to puncture the tissue, wherein each of the electrodes consists of a metal substantially circular surface separated one from another by insulation.
Preferably, the RF energy has a single phase.
Preferably, the method further comprises the step of independently and continuously adjusting the RF energy delivered to each electrode in response to a control signal from a programmable controlling device dependent on the temperature of the electrode.
In accordance with a fifth aspect of the invention, a method for treatment by radiofrequency (RF) ablation of tissue comprises the steps of:
generating RF energy;
providing one or more probes each comprising a plurality of separate electrodes and corresponding temperature sensors, each temperature sensor connected to a respective one of the plurality of electrodes;
measuring the temperature of each electrode using the respective temperature sensor;
splitting the RF energy into a plurality of separate channels, wherein each of the electrodes is coupled to a respective one of the plurality of channels; and
programmably controlling the splitting of the RF energy so as to independently control the ablation of tissue at each electrode using closed loop feedback of the measured temperature of the electrode. whereby the amount of the RF energy delivered to each electrode is independently regulated
Preferably, the method involves using at least two probes, and comprises the step of programmably controlling each of the probes separately.
In accordance with a sixth aspect of the invention, there is provided a method of splitting radio frequency energy delivered to one or more probes in a system for RF ablation of tissue. Each probe comprises a plurality of separate electrodes and corresponding temperature sensors for sensing the temperature of the electrode. The method comprises the steps of:
receiving RF energy from an RF energy generator;
providing a plurality of channel modules for separately delivering the RF energy to a respective electrode of the plurality of electrodes of the one or more probes, further comprising, for each channel module, the sub-steps of:
variably adjusting an amount of the RF energy delivered to the respective electrode in response to a control signal;
measuring the temperature of the respective electrode using the corresponding temperature sensor to provide a temperature signal;
determining if the temperature at the respective electrode exceeds a predetermined threshold and interrupting delivery of the RF energy to the respective electrode if the threshold is exceeded;
wherein each channel module is capable of receiving the respective control signal from and providing the respective temperature signal to a programmable controller so that the amount of the RF energy delivered to each electrode can be independently regulated using closed loop feedback of the temperature of each electrode.
Preferably, the step of variably adjusting the RF energy comprises the step of changing the resistance of a fast-switching variable resistance incorporated in a bridge rectifier in response to the control signal.
Preferably, the step of interrupting the RP energy comprises the steps of interrupting a current to the respective electrode and limiting the current.
Preferably, the step of determining comprises the step of comparing the temperature signal with the predetermined threshold.